1. Field of the Invention
The present invention relates to a display apparatus, and more specifically, to a structure and manufacturing method of a so-called active matrix display apparatus.
2. Description of the Related Art
A display apparatus, as an interface between a person and a computer, has been studied with respect to various display modes, so as to satisfy a growing demand in the information technology society for higher response speeds to enable reproduction of moving pictures with high contrast and reality.
Among other conventional display modes, an active matrix mode, where control is provided by placing an active device on each pixel, has been mainly used, and will be an important technique.
An active matrix mode using thin film transistors (hereinafter referred to as xe2x80x9cTFTsxe2x80x9d), in which Si is used as an impurity semiconductor material, is an especially important technique not only for liquid crystal display devices but also for other display devices such as organic electroluminescence (hereinafter referred to as xe2x80x9cELxe2x80x9d) devices.
Furthermore, Japanese Laid-open Publication Nos. 7-22706 and 7-86691 describe an emissive display apparatus using a surface emitting laser.
As shown in FIG. 3, an active matrix display apparatus includes a plurality of intersecting signal electrodes 5 and a plurality of switching devices 6 (such as TFTs) provided on a substrate 1.
There is a class of active matrix display modes in which an electric field is applied to a medium (e.g., a liquid crystal or an organic EL light-emission layer) through an electrode coupled to each switching device 6. In another class of active matrix display modes, the switching devices 6 themselves emit light (e.g., surface emitting laser display devices). A surface emitting laser device is produced on a compound crystal substrate, e.g., GaAs.
The above-described transistor or surface emitting laser composed essentially of impurity semiconductor materials (e.g., Si or GaAs) is usually produced from a single crystal. However, TFTs used for liquid crystal display devices are currently produced from amorphous Si for the following reasons. Firstly, in order to produce a large-size display apparatus, it is difficult to produce a single crystal adapted to such a large size. Therefore, a large-size Si substrate is prepared by first subjecting Si to plasma-disintegration and then depositing the resultant amorphous Si on the substrate. Secondly, if the substrate is required to be transmissive, as in the case of liquid crystal displays, it is necessary to provide Si on a glass substrate.
Since the amorphous state is occupied by countless grain boundaries which would not appear in a single crystal state, movement of carriers is inhibited, thereby considerably reducing carrier mobility. Thus, amorphous Si, which is currently used for liquid crystal display devices, cannot exploit the ability of a single crystal (Si) impurity semiconductor material, which have initially found application in LSIs. Moreover, polycrystal Si, which includes fewer grain boundaries and has higher carrier mobility than amorphous Si, began to be used recently, but its performance is considerably inferior to that of single crystal Si.
For a small-size substrate, it is within current practice to produce an active matrix array of impurity semiconductor devices directly on a single crystal, such as Si or GaAs (see Japanese Laid-open Publication Nos. 7-22706 and 7-86691). However, as described in Japanese Laid-open Publication No. 7-22706, such a small-sized substrate can only be used, for example, as a part of a projector-type expansion display apparatus. It is difficult to use the techniques described in Japanese Laid-open Publication No. 7-22706 to produce a direct-view type large display apparatus.
Japanese Laid-open Publication No. 5-249496 describes a method for providing a MOS transistor produced from a single crystal Si on a transmissive substrate. However, it is also essentially impossible to use this method to produce a display device, larger than the original single-crystal substrate (wafer), because the size of such a substrate is predetermined. While more and more display devices having a size exceeding 20 inches are being marketed, the maximum size of Si wafers still remains unchanged at a diameter of 8 inches.
Producing an active matrix array of impurity semiconductors, such as single-crystal Si or GaAs compounds, which is independent from substrate size can provide a display apparatus having much higher performance and reliability than is currently possible.
However, due to the above-described problems concerning the size of single-crystal substrates, such as Si or GaAs, the current techniques cannot produce a large direct-view type display apparatus. The current maximum wafer diameter is 8 inches for single-crystal wafers of Si and 5 inches for single-crystal compound wafers such as GaAs. Thus, it is essentially impossible with the current techniques to produce a large display device having a size of 30 inches or more, e.g., HDTV devices.
According to one aspect of the invention, there is provided a display apparatus including at least one substrate; a plurality of signal lines provided on the at least one substrate; and a matrix arrangement of a plurality of active devices fixed on the at least one substrate, wherein each of the plurality of active devices is formed on a semi-insulative crystal.
In one embodiment of the invention, the plurality of active devices are MOS transistors formed from single-crystal Si.
In another embodiment of the invention, the plurality of active devices are surface emitting lasers formed from crystals of a GaAs compound.
According to another aspect of the invention, there is provided a method for manufacturing a display apparatus, including the steps of: producing a plurality of active devices on a semi-insulative crystal; reducing a thickness of the crystal from a lower face thereof to attain a predetermined thickness; isolating the plurality of active devices from one another; forming a plurality of holes in a second substrate adapted to a matrix arrangement in which the plurality of active devices are to be deployed on a display apparatus; placing the plurality of active devices into the plurality of holes; and after the plurality of active devices are placed into the plurality of holes, pressing the second substrate against a first substrate on which a plurality of wires are formed, thereby transferring the plurality of active devices onto the first substrate and connecting each of the plurality of wire to a corresponding one of the plurality of active devices.
In one embodiment of the invention, the plurality of active devices are MOS transistors formed from single-crystal Si.
In another embodiment of the invention, the plurality of active devices are surface emitting lasers formed from crystals of a GaAs compound.
According to the present invention, it is possible to produce an active matrix array of semiconductor materials, such as a single-crystal Si or GaAs compound, regardless of the size of a substrate. Thus, it is possible to produce a TFT active matrix array substrate of high-performance transistors of single-crystal Si and an auto-emission active matrix display apparatus having a large-size substrate.
Thus, the invention described herein makes possible the advantage of providing a production method for a large display apparatus, including active devices having significantly higher performance than those of conventional amorphous or polycrystal active devices.
This and other advantages of the present invention will become apparent to those skilled in the art upon reading and understanding the following detailed description with reference to the accompanying figures.